Such milling tools are used in actual practice in order to produce prototypes for printed circuit boards. Here, data from a CAD program can be directly converted into control data for the machining head of the milling tool so that a functional printed circuit board can already be made within a short period of time. A galvanic treatment is not necessary here since the structures are created directly by milling off part of the conductive substrate surface by means of the milling tool. In order to set the width of the track to be milled off, the penetration depth of the tapered milling tool used for this purpose can be changed by varying the distance.
The prior-art methods are capable of creating structures with a conductor track spacing and a conductor track width of 100 μm as well as a bore diameter of 150 μm. The areas of application are very multifaceted. For example, differing rigid and flexible materials as well as soft substrates known from HF and microwave technology can be processed into prototypes that are then virtually ready for serial production.
Prototypes that can be reproduced as often as desired can be made within a very short period of time and are thus available either for testing or for small-volume production. Moreover, it is very easy to mill cutouts in the printed circuit boards or else to cut printed circuit boards out of the base material—even with complex contours—and the same holds true for the production of masking lacquer for printed circuit board prototypes.
Depending on the application purpose, different milling tools, especially with different total lengths, can be used in actual practice. For this reason, before the machining of the substrate is started, the distance between the milling tool tip and the milling head has to be determined, particularly in order to be able to set the penetration depth of the milling tool with reproducible precision.
For this purpose, for example, it is a known procedure to move the milling head that secures the milling tool so that it comes into contact with a touch sensor, for instance, a momentary-contact switch, by means of which a signal to a control unit is triggered when contact is made. The position of the milling tool derived from this is then taken as the reference value, especially for the Z-axis of the subsequent machining step.
Moreover, it is already a known procedure to place the milling tool that is secured on the milling head against an electrically conductive element. A corresponding signal is triggered as soon as a sensor detects a flow of current between the conductive element and the milling tool.
Within the scope of a method and a device for the measurement and fine adjustment of a tool in a tool holder according to German patent application DE 103 45 993 A1, on the basis of the actual position that was detected and of the corrected tool position that was determined by calculation, a correction is made by means of a fine adjustment of the tool in the tool holder. Piezoelectrically active micro-actors, for example, are employed for this purpose. Here, the tool is moved by means of the actors, together with the tool holder that secures the tool.
German patent application DE 40 30 176 A1 describes a method for calibrating a tool. For this purpose, the tool is moved from a starting position to a reference surface until contact is made with it. Upon contact, the occurring audio signals are detected and subsequently converted into electric signals. These are then fed to a computing unit in order to determine a precise starting position of the machining tool with respect to the workpiece or to determine a correction parameter for the tool advance that takes into account the detected starting position.
Moreover, German patent application DE 197 09 136 A1 relates generally to a method for micro-structuring a substrate with a milling tool.